How many cast on stitches for an afghan?

I’m trying to make an afghan without a pattern, just do whatever as it goes along. If I use med. worsted weight yarn and a 15 circ needle, how many stitches would I be casting on?

What is your gauge and how big an afghan do you want?

I didn’t do a gauge, should I? I just wanted to cast on and go!

Well if you do a gauge swatch, you can have a better idea of what size you’ll end up with. If you’re using a worsted weight yarn and a size 15 needle, that will be a VERY loose knit. Is that what you’re wanting? I’m doing a worsted weight afghan on size 8 needles and with a 200 stitch cast on, it is working out to be about 45" across.

Say you do a swatch and get, for example, 4sts/1". Then you can figure that if you cast on 200sts you would wind up with 50" across. You can adjust your cast on up and down to get whatever finished size you want.

Thank you knitqueen, I think I’ll try it your way, sounds less complicated.

Just CO 20 sts and do several rows. Then measure 3-4" in the middle and figure out how many sts/inch that makes. Then multiply the sts/inch times the inches you want for the width - 40-45-50? - and CO that many. Worsted weight can definitely be knit with larger than size 8, I use anywhere from 10s to 11s including the metric sizes in between. But it would be a pretty loose st on 15 and snag easily. If you doubled the yarn, it’ll work out well on 15s, or if you use bulky yarn.